How do you say in English "i'm merely a clown for the media " ?

Hahahahahahahaha

Just like you wrote it is perfectly understandable English, IMHO.

"Hello, I'm Boris Johnson.............."

That roughly translates to: :

"Hi, my name is Joe Biden" 

i'm joe biden.....................

Gee.  I don't know.

It doesn't make sense.

It's somewhat understandable for most USA English speakers, but it's not a particularly precise way of indicating the idea that you're trying to convey. Actually, I don't know exactly what you're trying to say, and I doubt if anybody much in USA would describe themselves as clowns for the media.